A FBI source confirms to The Hollywood Reporter that FBI agents -- along with police, fire and health officials -- responded to the report of a suspicious mailing at the CBS Studios set of the ABC competition. Field tests indicated the substance in question was innocuous, but further tests are underway at a local lab and an investigation into who sent the package is ongoing.

Though no further information was provided, the initial TMZ report said the package was accompanied by a note that read something to the effect of "This is what will happen to you if Bristol Palin stays on [the show]."

The white powder inside the package was deemed to be harmless by law enforcement, but they're treating it as a serious investigation.

Palin, the daughter of former Alaska governor Sarah Palin, has courted controversy since joining the series for the first time in 2010. A similar package containing white powder arrived at the Los Angeles studio where the live show films on Mondays and Tuesdays. Her return for the All-Stars season had thus far not caused nearly as much media drama.

ABC had no comment on the matter, and CBS and producers at BBC Worldwide did not comment on the actual situation, but BBC did release the following statement: "BBC Worldwide Productions takes the health and safety of all our competitors and employees very seriously."

Palin and partner Mark Ballas were spared elimination from the series during Tuesday's results show, despite having the lowest scores during the week's performance.